(1) Field of the Invention
The main object of the invention is an array of optically-controlled elements for the diffusion of electromagnetic energy.
The object of the invention is also an array providing for the diffusion of ultra-high frequency energy in a near field. In the prior art, controllable, diffusing arrays are made with radiating element charged by variable impedances. For example, electronically-controlled diodes are used. In the absence of any control signal, an electromagnetic wave illuminating the array is reflected and/or diffused without any change in frequency.
A modulated state of the array is obtained by modulating the impedance of the charges at a frequency f.sub.m of one or more elements of the array.
In a first example, the modulation of certain diffusing elements is a phase modulation. In this case, a frequency wave f.sub.0 illuminating the array will be diffused with a spectrum of lines and the frequency will be equal to f.sub.0 +kf.sub.m, k being an integer.
In a second example, the modulation is a pure amplitude modulation. In this case, the waves diffused by the array comprise, in addition to the spectral line at the frequency f.sub.0, the spectral line f.sub.0 +f.sub.m as well as the spectral line corresponding to the frequency f.sub.0 -f.sub.m.
(2) Description of the Prior Art
The device of the prior art comprises an electrical control for the modulation of diodes organized in matrix form. A device of this type is described in the French patent No. 81 09855. A diode, for example the diode at the intersection of the row I and the column J, is controlled by receiving a signal simultaneously at the row I and the column J. Thus the device very greatly reduces the number of connections needed.
Devices of the prior art have disadvantages. Firstly, the matrix-based control system prevents the possibility of having individual controls for several diodes.
Secondly, the length of the modulation current input lines prevents the obtaining of high-frequency modulations for large-sized panels. For example, it is practically impossible to exceed 100 MHz for panels with areas of more than one square meter.
Furthermore, it is extremely difficult to build modulation circuits: making such circuits means that it should be possible to supply power to any one of the columns and rows. It is therefore necessary to make a branching device comprising several outputs. For example, an array with an increment of 20 mm., with an area of 2 m. by 2 m., comprises 100 columns and 100 rows.
In the device according to the invention, each radiating element is associated with a diode, the modulation control of which is provided by a photoreceptor. To modulate a given element, a light wave is received by the photodetector which is connected to the corresponding radiating element. The light wave is emitted, for example, by laser. Power is supplied to several radiating elements simultaneously by modulating several photoreceptors with, for example, several lasers. The control of each radiating element is completely independent.